Defect-free junction formation using octadecaborane self-amorphizing implants

ABSTRACT

A method and apparatus for implanting a semiconductor substrate with boron clusters. A substrate is implanted with octadecaborane by plasma immersion or ion beam implantation. The substrate surface is then annealed to completely dissociate and activate the boron clusters. The annealing may take place by melting the implanted regions or by a sub-melt annealing process.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/563,764 filed Sep. 21, 2009.

FIELD

Embodiments described herein relate to semiconductor manufacturingmethods. More specifically, embodiments of the invention encompassmethods of doping semiconductor substrates.

BACKGROUND

As semiconductor technology progresses, devices formed on semiconductorsubstrates grow smaller. As devices grow smaller, manufacturers arecontinually challenged to develop productive processes for making thedevices. Currently, manufacturing processes are being deployed to makedevices having critical dimension of 45 nm. Researchers are busydeveloping next generation processes for devices having criticaldimension of 20 nm or less. At these extreme dimensions, implantingdopants in a substrate becomes forbidding. In a traditional boron dopingprocess, for example, boron atoms are directed toward a substrate withsufficient energy to penetrate the crystal lattice to a desired depth,and the substrate is then annealed to distribute the boron and activateit (attach it to the crystal network). As device dimensions growsmaller, control of implantation depth becomes more critical. Nextgeneration devices are expected to have junctions no more than about 50atomic layers deep.

Implantation problems arise as junction depth diminishes. Because theions must travel more slowly to avoid implanting too deeply, therepulsive charge among like-charged ions forces them to diverge fromtheir intended path. To compensate for this effect, fast-moving ions aremagnetically decelerated near the surface of the substrate. Beamdeceleration, however, results in “energy contamination,” arising fromexchange of charge between fast-moving ions and fugitive neutralparticles during or prior to deceleration. The fast-moving neutralizedparticles are unaffected by the beam decelerator and implant deeply intothe substrate.

Small ions also channel through the crystal lattice. Because the crystallattice has open spaces large enough for many ions to pass unimpeded,more ions will travel down these “channels”, resulting in highlyvariable implant depth. To reduce the tendency to channel, manymanufacturers have resorted to “pre-amorphizing” the substrate surfaceto remove any opportunity for channeling. Pre-amorphization may alsoimprove implant dose by opening more space within the solid matrix forions to penetrate. Pre-amorphized substrates require more annealing,however, to activate dopants because the crystal structure is completelydisrupted to a considerable depth and must be repaired. This leads tounwanted dopant diffusion and residual EOR damage.

Thus, there is a continuing need for better methods of implantingdopants in a shallow junction with high dopant dose and activation, lowsheet resistance, and even distribution of dopants.

SUMMARY

Embodiments described herein provide a method of treating a substrate,comprising implanting boron macromolecules into a surface of thesubstrate, melting the surface of the substrate implanted with the boronmacromolecules, resolidifying the surface of the substrate implantedwith the boron macromolecules, and annealing the surface of thesubstrate. In some embodiments, the boron macromolecules comprise boronclusters having at least sixteen boron atoms.

Other embodiments provide a method of treating a substrate, comprisingimplanting octadecaborane into the surface of the substrate, andannealing implanted regions of the substrate by repeatedly heating andcooling the implanted regions.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentinvention can be understood in detail, a more particular description ofthe invention, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments and are therefore not to be considered limiting inscope, because other equally effective embodiments may be devised.

FIG. 1A is a schematic cross-sectional view of an apparatus according toone embodiment.

FIG. 1B is a perspective view of the apparatus of FIG. 1A.

FIG. 2 is a flow diagram summarizing a method according to oneembodiment.

FIG. 3 is a flow diagram summarizing a method according to anotherembodiment.

FIG. 4 is a schematic illustration of an anneal system that may be usedto practice embodiments described herein.

FIG. 5 is a schematic illustration of a top view of a substrate thatcontains forty square shaped dice that are arranged in an array.

FIG. 6 is a flow diagram summarizing a method according to anotherembodiment.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

Embodiments described herein generally provide methods of doping asemiconductor substrate with boron. A substrate is provided to animplant chamber. A gas mixture containing boron macromolecules isprovided to the chamber. The boron macromolecules are ionized andaccelerated toward the substrate with energy selected to accomplish ashallow implant of the boron macromolecules into a surface of thesubstrate. The boron macromolecules penetrate and amorphize thesubstrate surface and break apart into atoms or small clusters. Theboron dopant is then activated using an anneal process.

FIG. 1A depicts a plasma reactor 100 that may be utilized to practiceion implantation, oxide layer formation, and capping layer formationaccording to one embodiment of the invention. One suitable reactor whichmay be adapted to practice the invention is a P3i™ reactor, availablefrom Applied Materials, Inc., of Santa Clara, Calif. Another reactorwhich may be adapted to practice the invention is described in U.S.patent application Ser. No. 11/608,357. It is contemplated that themethods described herein may be practiced in other suitably adaptedplasma reactors, including those from other manufacturers.

The plasma reactor 100 includes a chamber body 102 having a bottom 124,a top 126, and side walls 122 enclosing a process region 104. Asubstrate support assembly 128 is supported from the bottom 124 of thechamber body 102 and is adapted to receive a substrate 106 forprocessing. A gas distribution plate 130 is coupled to the top 126 ofthe chamber body 102 facing the substrate support assembly 128. Apumping port 132 is defined in the chamber body 102 and coupled to avacuum pump 134. The vacuum pump 134 is coupled through a throttle valve136 to the pumping port 132. A gas source 152 is coupled to the gasdistribution plate 130 to supply gaseous precursor compounds forprocesses performed on the substrate 106.

The reactor 100 depicted in FIG. 1A further includes a plasma source 190best shown in the perspective view of FIG. 1B. The plasma source 190includes a pair of separate external reentrant conduits 140, 140′mounted on the outside of the top 126 of the chamber body 102 disposedtransverse to one another (or orthogonal to one another, as shown in theexemplary embodiment depicted in FIG. 1B). The first external conduit140 has a first end 140 a coupled through an opening 198 formed in thetop 126 into a first side of the process region 104 in the chamber body102. A second end 140 b has an opening 196 coupled into a second side ofthe process region 104. The second external reentrant conduit 140 b hasa first end 140 a′ having an opening 194 coupled into a third side ofthe process region 104 and a second end 140 b′ having an opening 192into a fourth side of the process region 104. In one embodiment, thefirst and second external reentrant conduits 140, 140′ are configured tobe orthogonal to one another, thereby providing the two ends 140 a, 140a′, 140 b, 140 b′ of each external reentrant conduits 140, 140′ disposedat about 90 degree intervals around the periphery of the top 126 of thechamber body 102. The orthogonal configuration of the external reentrantconduits 140, 140′ allows a plasma source distributed uniformly acrossthe process region 104. It is contemplated that the first and secondexternal reentrant conduits 140, 140′ may be configured as otherdistributions utilized to provide uniform plasma distribution into theprocess region 104.

Magnetically permeable torroidal cores 142, 142′ surround a portion of acorresponding one of the external reentrant conduits 140, 140′. Theconductive coils 144, 144′ are coupled to respective RF plasma sourcepower generators 146, 146′ through respective impedance match circuitsor elements 148, 148′. Each external reentrant conduit 140, 140′ is ahollow conductive tube interrupted by an insulating annular ring 150,150′ respectively that interrupts an otherwise continuous electricalpath between the two ends 140 a, 140 b (and 140 a′, 104 b′) of therespective external reentrant conduits 140, 140′. Ion energy at thesubstrate surface is controlled by an RF plasma bias power generator 154coupled to the substrate support assembly 128 through an impedance matchcircuit or element 156.

Referring back to FIG. 1A, process gases including gaseous compoundssupplied from the process gas source 152 are introduced through theoverhead gas distribution plate 130 into the process region 104. RFplasma source power generator 146 is coupled from the power applicatorto gases supplied in the conduit 140, which creates a circulating plasmacurrent in a first closed torroidal path including the externalreentrant conduit 140 and the process region 104. Also, RF plasma sourcepower generator 146′ may be coupled from the other power applicator togases in the second conduit 140′, which creates a circulating plasmacurrent in a second closed torroidal path transverse (e.g., orthogonal)to the first torroidal path. The second torroidal path includes thesecond external reentrant conduit 140′ and the process region 104. Theplasma currents in each of the paths oscillate (e.g., reverse direction)at the frequencies of the respective RF plasma source power generators146, 146′, which may be the same or slightly offset from one another.

In one embodiment, the process gas source 152 provides different processgases that may be utilized to provide ions implanted to the substrate106. The power of each plasma source power generator 146, 146′ isoperated so that their combined effect efficiently dissociates theprocess gases supplied from the process gas source 152 and produces adesired ion flux at the surface of the substrate 106. The power of theRF plasma bias power generator 154 is controlled at a selected level atwhich the ion energy dissociated from the process gases may beaccelerated toward the substrate surface and implanted at a desireddepth below the top surface of the substrate 106 with desired ionconcentration. For example, with relatively low RF power, such as lessthan about 50 eV, relatively low plasma ion energy may be obtained.

A gas mixture comprising boron macromolecules is provided to a chamberhaving a substrate disposed therein. Embodiments of the invention mayalso be practiced using a QUANTUM® X Plus implanter available fromApplied Materials, Inc., of Santa Clara, Calif., or equivalent devicesfrom other manufacturers. The boron macromolecules may comprise anymixture of stable boron macromolecules, including but not limited to theboron hydrides B_(x)H_(y), wherein x is between about 6 and about 20,and y is between about 12 and about 24. In many embodiments, boronclusters or macromolecules used for implantation will have at least 16boron atoms each. Some exemplary boron hydride macromolecules includeoctadecaborane (B₁₈H₂₂), decaborane (B₁₀H₁₄), hexaborane (B₆H₁₀),octaborane (B₈H₁₂), and hexadecaborane (B₁₆H₂₀). Octadecaborane ispreferred because it may be ionized without decomposing under processingconditions. Octadecaborane also transports a high quantity of boron to asubstrate at very low energy without the difficulties enumerated above.Because octadecaborane ions have a high mass-to-charge ratio, thetendency for the ions to diverge is sharply reduced, allowing low energyimplant with none of the challenges described above.

In one embodiment, octadecaborane (B₁₈) is vaporized by heating to asublimation temperature. B₁₈ may be vaporized using a Clusterlon®vaporizer available from SemEquip, Inc., of North Billerica, Mass., orequivalent source systems available from other manufacturers. The B₁₈vapor is then provided to a chamber or device for implanting into asurface of a substrate.

In a plasma-immersion type device, the B₁₈ vapor is provided to anionizing zone formed inside a gas distribution apparatus. RF power iscoupled to the ionizing zone to ionize the B₁₈. Typically, flow of acarrier gas will be established at between about 1,000 sccm and about5,000 sccm, such as between about 2,000 sccm and about 4,000 sccm, forexample about 3,000 sccm. The carrier gas may be any gas non-reactiveunder processing conditions, such as helium or argon. RF power iscoupled into the gas flow, and then a pulse of B₁₈ vapor is provided tothe chamber to form a gas mixture in the gas distribution apparatus. Thepulse of B₁₈ vapor may be provided for about 1 second at a flowratebetween about 500 sccm and about 2,000 sccm, such as between about 700sccm and about 1,200 sccm, for example about 1,000 sccm. The ionizing RFpower may be coupled into the ionizing zone at between about 100 W andabout 500 W, such as between about 200 W and about 400 W, for exampleabout 300 W. The RF power may be coupled into the ionizing zone by useof capacitative coupling using, for example, parallel plate electrodes,or by inductive coupling. In some embodiments, greater than 90% of theB₁₈ molecules are ionized, such as greater than 95%, for examplergreater than 99%.

The B₁₈ ions flow through the ionizing zone into the chamber through thegas distribution apparatus. In some embodiments, the B₁₈ ions may beaccelerated toward the substrate surface by application of an electricalbias to the gas distributor, the substrate support, or both. The biasmay be a DC bias or an RF bias. Some embodiments use no electrical bias,allowing the B₁₈ ions to drift toward the substrate with the gas flow.In embodiments wherein an electrical bias is used, a bias of 100 V to300 V DC or root-mean-square RF at a power level of 10 W to 500 W may beused. In some embodiments, 200 V DC is provided at 100 W of power.

In an ion implanter device, B₁₈ vapor is passed through an ionizing zonein which an electric field ionizes the B₁₈ molecules. A magnetic massselector produces a beam of B₁₈ ions which are focused and directedtoward the substrate. Each boron cluster will generally have kineticenergy between about 2 keV and about 20 keV, which is equivalent to eachboron atom having kinetic energy between about 0.1 keV and about 1.1keV. The beam current may be between about 0.1 mA and about 5.0 mA todeliver equivalent ion current between about 2 mA and about 100 mA ofindividual boron ions.

Octadecaborane ions disrupt the crystal structure of a substrate surfaceas they implant, and are thus self-amorphizing. The large ions impactthe substrate surface, substantially melting the surface in theimmediate vicinity of the impact. As the ions pass into the surface,they form tiny impact craters, substantially disrupting the crystallattice. Hydrogen atoms are stripped from the ion and diffuse out of thesubstrate, leaving the boron cluster to barrel through successive layersof the crystal surface. As the large clusters move through the crystal,fragments of boron break off from the main cluster. These fragments maybe single boron atoms or clusters of a few boron atoms. The smallclusters are better able to penetrate the crystal lattice with lowenergy by channeling through the empty spaces, but because the largecluster is amorphizing its immediate environment, movement of most smallclusters is diverted laterally, causing lateral dispersion of boronatoms.

The inventors have found that annealing processes involving melting thesurface of the substrate, and sub-melt annealing processes involvingrapid repeated heating and cooling are more effective for activatingboron macromolecule implants than traditional sub-melt anneal processes.While not wishing to be bound by theory, it is thought that implantationof B₁₈ clusters amorphize the surface of the substrate to a degree muchgreater than implantation of smaller particles, so that standardsub-melt anneal processes do not fully recrystallize the substrate.Additionally, B₁₈ clusters do not necessarily fragment entirely intoindividual boron atoms upon implantation, so melting assists incompleting the fragmentation in-situ. In some embodiments, due to theability of B₁₈ clusters to amorphize the surface of a substrate withoutcreating EOR defects, ultra-shallow junctions having little or noleakage due to EOR defects may be created using B₁₈ implantationfollowed by melt annealing.

FIG. 2 summarizes a method 200 of doping a substrate with boronaccording to one embodiment of the invention. Boron macromolecules areimplanted into the surface of the substrate at 202. Octadecaborane orother stable macromolecules containing a large amount of boron, such as,but not limited to, icosaborane (B₂₀H₂₆), triantaborane (B₃₀H_(x)), andsarantaborane (B₄₀H_(x)) may be useful for certain embodiments.Combinations or mixtures of the above may also be used. Implantation maybe accomplished using a plasma immersion apparatus or a beam implantapparatus to ionize the boron clusters and direct them toward thesubstrate. A DC or RF bias may be applied to the substrate to tune theimplant energy.

The implanted portion of the substrate surface is melted at 204. A meltheating process suitable for treatment of substrates implanted withoctadecaborane may be administered using any convenient source ofenergy. A substrate may be heated by conduction or by radiant heatingwith electromagnetic radiation. The substrate may be disposed on aheated support or may be subjected to irradiation with visible,infrared, or microwave radiation. A heated support may be heated usingresistive heating embedded within the support, or by providing conduitswithin the support for flowing hot fluids. The radiation may be coherentor incoherent, focused or unfocused, monochromatic or polychromatic, orpolarized or unpolarized to any degree. The radiation may be deliveredby any combination of one or more lasers, flash lamps, arc lamps, orfilament lamps. In some embodiments, the entire substrate may be treatedat once, while in other embodiments, portions of the substrate may betreated consecutively. In some embodiments, an energy absorbing film,such as a carbon film, may be applied over the substrate to improveapplication of energy to the substrate surface, and to reduce loss ofboron from sublimation as the substrate is heated. In some embodiments,the substrate surface may be heated with radiant energy while the bulkof the substrate is cooled using a cool support.

The portion of the substrate implanted with octadecaborane is heated toa temperature at or above the melting point of the implanted portion. Insome embodiments, only the implanted surface is melted, while the bulkof the substrate remains crystalline. Due to the extent of amorphizingaccompanying octadecaborane implantation in some embodiments, it may besufficient to heat the surface to a temperature at or above the melttemperature of the amorphous material, which will generally be less thanthat of the corresponding crystalline material. For embodiments in whicha silicon substrate is treated, a temperature of 1,200° C. or more maysuffice to melt the amorphized portion of the surface. Because amorphoussilicon melts at a lower temperature than crystalline silicon, theamorphized portion melts at this temperature, but the underlyingcrystalline phase does not. To minimize any substrate damage due tothermal stress, it may be advantageous to heat the bulk of the substrateto an intermediate temperature. In an exemplary embodiment, thesubstrate support may heat the substrate to a temperature of 500° C. ormore, and a radiant energy source may be used to heat portions of thesubstrate to the melt temperature. Very fast heating of the melt zone isgenerally preferred to achieve melting of the amorphous phase before itcrystallizes. In some embodiments, nanosecond pulsed lasers having pulseduration from a few nanoseconds to about 200 nanoseconds, such asbetween 10 nsec and 100 nsec, for example 20 nsec, may be used to meltthe amorphous phase.

After melting, the melted portions of the substrate are recrystallizedat 206. In many embodiments, the recrystallization is performed in a waythat promotes formation of a crystal lattice including the implantedboron atoms. In this way, the recrystallization is similar to anannealing process. To promote crystal formation, it is generallypreferred to cool the melted portions at a rate slower than would beachieved through normal conductive or radiative cooling. In someembodiments, it may be advantageous to maintain the temperature of thesubstrate at 500° C. or more for up to 10 minutes, such as between about1 minute and about 10 minutes, for example about 3 minutes, followingmelting. In other embodiments, it may be useful to cool the implantedportion of the substrate surface at a rate not higher than about 100°C./sec, such as between about 1° C./sec and about 50° C./sec, forexample about 10° C./sec. In still other embodiments, a slow coolingrate may be combined with periods of constant temperature to accomplishthe recrystallization.

A substrate to be implanted as described herein may be subjected to apreclean process. The solution may have a concentration of about 0.1 toabout 10.0 weight percent HF and be used at a temperature of about 20°C. to about 30° C. In an exemplary embodiment, the solution has about0.5 weight percent of HF and a temperature of about 25° C. In anotherexemplary embodiment, the solution has about 1.0 weight percent of HFand a temperature of about 25° C. The substrate may be exposed to the HFsolution form a duration from about 10 seconds to about 60 seconds. Anyunwanted oxide is removed from the substrate by the etching action ofthe HF solution. A brief exposure of the substrate to the solution maybe followed by a rinse step in de-ionized water and a bake step. Thebake step may be performed under an inert atmosphere, such as nitrogengas, helium, or argon, at a temperature selected to volatilize anyremaining fugitive species from the surface of the substrate. In oneembodiment, the substrate may be exposed to a temperature of betweenabout 200° C. and about 600° C. for about 60 seconds.

A substrate implanted with boron as described herein may be subjected toa stripping process following the anneal process to remove any residualhigh surface concentration of boron. In some embodiments, the substrateis exposed to a hydrogen-containing gas to generate volatile hydrides.In some embodiments, the hydrogen-containing gas may be a plasma. Forexample, hydrogen gas or ammonia, with or without plasma, may be used toconvert dopants at the surface of the substrate into volatile hydrides.Boron may react to form various volatile boron hydrides such as borane,diborane, or other volatile borane oligomers. In one exemplaryembodiment, the substrate may be exposed to a hydrogen plasma forbetween about 10 seconds and about 30 seconds, such as about 15 seconds,at a temperature of between about 100° C. and about 300° C., such asabout 200° C., to reduce the surface concentration of dopants. Thehydrogen plasma may be generated in-situ or remotely, and may accompanya non-reactive carrier gas such as argon or helium. The carrier gas flowmay be established at a rate between about 1,000 sccm and about 2,000sccm, such as about 1,500 sccm, and a pulse of hydrogen gas added. Thepulse of hydrogen gas may be supplied at a flow rate between about 100sccm and about 500 sccm, such as about 300 sccm, for an interval ofabout 10 seconds to about 30 seconds, such as about 15 seconds.Following exposure, the hydrogen gas is stopped and the carrier gaspurges any remaining volatile hydrides from the chamber. The chamber mayalso be pumped-down to a low pressure to remove any remaining fugitivehydrides.

FIG. 3 summarizes a method 300 according to another embodiment of theinvention. A substrate is disposed in a processing chamber at 302. Flowof a carrier gas is established at 304. The carrier gas may be anynon-reactive gas, such as helium, argon, or nitrogen gas. In someembodiments, the carrier gas flow rate may be between about 1,000 sccmand about 5,000 sccm, such as between about 2,000 sccm and about 4,000sccm, for example about 3,000 sccm. A precursor comprising boronmacromolecules is added at 306. The boron precursor may be added to thecarrier gas stream outside the processing chamber or may be addeddirectly to the processing chamber. The boron precursor may be providedat a flow rate between about 100 sccm and about 500 sccm, such asbetween about 200 sccm and about 400 sccm, for example about 300 sccm.The boron precursor will generally be provided at or above avaporization temperature to maintain the boron precursor in a vaporstate. For B₁₈, the boron precursor may be provided at a temperaturebetween about 100° C. and about 400° C., such as about 250° C.

The carrier gas and boron precursor flow into one or more ionizing zonesnear or within the processing chamber. At 308, ionizing energy isapplied to ionize the boron precursor without decomposing the boronmacromolecules, which then emerge through a gas distributor into theprocessing chamber. In some embodiments, the ionizing energy may beapplied by coupling an electric field into the ionizing zones. Theelectric field may be static, such as a DC bias, or varying, such asthat generated by application of RF power, and may be coupled into theionizing zones by capacitative or inductive means. In one embodiment,inductive ionizing zones are provided outside the processing chamber,with one or more conduits to carry gas to the ionizing zones from theprocessing chamber. An electric field is coupled into each ionizing zoneby providing one or more torroidal cores disposed around the ionizingzones. The one or more torroidal cores are energized with RF power togenerate an electric field inside the ionizing zones. For mostembodiments, the ionizing energy may be provided at a power level ofbetween about 100 W and about 500 W, such as about 300 W.

At 310, an electric field may be applied to accelerate the ionized boronmacromolecules toward the substrate surface. This may be a static field,such as a DC bias applied to the substrate support, the gas distributor,or both, or it may be a varying field such as an RF-driven field.Application of an electric field is an optional step used to adjust theenergy of the ionized boron macromolecules as they travel toward thesubstrate surface. Some embodiments may allow the ions to drift towardthe surface. If an electric field is used, it will preferably be a weakfield, applied at a power level between about 50 W and about 500 W, suchas about 100 W. In some embodiments, the ionized boron macromoleculeswill travel toward the substrate surface with kinetic energy betweenabout 100 eV and about 2,000 eV. Individual embodiments may energize theions with any particular value or range of kinetic energy between thesetwo values. A single embodiment may also feature ions with adistribution of energies within this range. For example, a first portionof the ionized boron macromolecules may have higher kinetic energy thana second portion of the ionized boron macromolecules due to thermal,pressure, or electrical gradients or fluctuations.

The ionized boron macromolecules impact the substrate disposed on thesubstrate support at 312, implanting into the substrate surface. Themacromolecules generally carry enough kinetic energy to disrupt thecrystal matrix of the substrate surface as they impact, amorphizing thesurface. Additionally, the boron macromolecules fragment as they boreinto the substrate surface. The fragments generally diverge laterallyfrom the main macromolecule due to the amorphizing process, resulting inan as-implanted concentration profile that is relatively abrupt. In someembodiments, the maximum concentration of as-implanted boron may bebetween about 5 and 15 nm below the surface, such as about 10 nm belowthe surface, and may be between about 10¹⁹ cm⁻³ and about 10²¹ cm⁻³ atthat depth. The as-implanted concentration will generally fall at a rateof 2-20 nm/dec., depending on the implant energy. The implant layer willgenerally be between about 30 nm and about 150 nm thick, such as about50 nm thick. The resulting implant layer will be completely amorphizedby action of the boron macromolecules, with boron atoms or small boronclusters of 2 to 4 boron atoms each, dispersed through the layer.

At 314, heating energy is applied to one or more implanted portions. Theheating energy is selected to raise the temperature of the implantedarea to the melting point, or above. The heating energy may be appliedin any convenient way. For example, electromagnetic energy or radiantenergy may be projected toward the implanted area to melt portionsthereof. Additionally, background heating may be applied to pre-heat theimplanted area, an area of the substrate containing the implanted areato be melted, or the entire substrate. For example, a heated substratesupport may apply conductive heating energy to the substrate to raiseits temperature to between about 400° C. and about 700° C., maintainingthat temperature while individual implanted areas are melted byapplication of incremental heating energy. Radiant energy for meltingimplanted areas may be delivered by laser, heat lamp, flash lamp, or thelike, and may be pulsed or continuous, coherent or incoherent,monochromatic or polychromatic, polarized or unpolarized to any degree.Portions of the substrate may be irradiated consecutively, or the entiresubstrate irradiated simultaneously. The implanted portions may beheated to a temperature between about 1,100° C. and about 1,400° C.,depending on the embodiment. Melting of amorphized silicon generallyoccurs at a lower temperature than melting of crystalline silicon, soembodiments wherein the substrate material is predominantly silicon mayfeature heating implanted portions to about 1,200° C. The melttemperature is selected to melt the amorphous layer without melting theunderlying crystalline layer. It is generally desired to heat theportions to be melted at a high rate, so that the amorphous portion isheated faster than heat can be conducted away by the substrate material,and is melted before it can recrystallize. When amorphous silicon isslowly heated to near its melting point, it undergoes solid phaseepitaxy, converting to crystalling silicon with a higher melting point.Very rapid heating may melt the amorphous portion before it canrecrystallize.

At 316, the temperature of the melted portions of the implanted surfaceis maintained above the melting temperature for a period of time toallow complete dissociation of remaining boron fragments and somediffusion of boron out of the maximum concentration layer. Mostembodiments using nanosecond pulsed lasers will feature melt durationfrom tens to hundreds of nanoseconds. In some embodiments, however, meltduration may be between a few milliseconds and about 0.5 seconds, suchas about 10 msec.

At 318, the heated portions of the substrate surface are cooled at acontrolled rate to recrystallize or resolidify the substrate surface. Ingeneral this cooling rate will be slower than would be experiencedthrough simple de-energizing of the heating apparatus to allowcontrolled recrystallization. This controlled recrystallization processeffectively activates the boron dopant atoms derived from the implantedboron macromolecules by moving them to crystal lattice positions andfreezing them in place. In some embodiments, heating energy may beapplied to melted implant areas control the rate of cooling of meltedimplant by adjusting the energy-time profile of the heating source. Forexample, the profile of the pulse of a nanosecond laser may be adjustedusing pulse modification optics, or the shape of a discharge voltagepulse applied to one or more flash lamps may be adjusted. The heatingenergy may be electromagnetic energy or radiant energy according to anyof the methods described above. In other embodiments, heating energy maybe applied to the entire substrate to maintain its temperature at anintermediate temperature for a period of time to accomplish therecrystallization process. For example, a substrate may berecrystallized by maintaining its temperature between about 400° C. andabout 700° C. for between about 1 minute and about 10 minutes. Forexample, in one embodiment, a substrate may be recrystallized bymaintaining its temperature at about 500° C. for about 60 seconds. Thecontrolled cooling process anneals the substrate surface to eliminatecrystal defects from the substrate surface, distribute the dopants, andactivate the dopants.

FIG. 4 schematically illustrates an anneal system 400 that may be usedto practice embodiments of the present invention. The anneal system 400comprises an energy source 420 which is adapted to project an amount ofenergy on a defined region, or an anneal region 412, of a substrate 410to preferentially melt certain desired regions within the anneal region412.

In one example, as shown in FIG. 400, only one defined region of thesubstrate 410, such as an anneal region 412, is exposed to the radiationfrom the energy source 420 at any given time. The substrate 410 movesrelative to the energy source 420 so that other regions on the substrate410 may be sequentially exposed to the energy source 420.

In one aspect of the invention, multiple areas of the substrate 410 aresequentially exposed to a desired amount of energy delivered from theenergy source 420 to cause the preferential melting of desired regionsof the substrate 410.

In general, the areas on the surface of the substrate 410 may besequentially exposed by translating the substrate 410 relative to theoutput of the energy source 420 (e.g., using conventional X/Y stages,precision stages) and/or translating the output of the energy source 420relative to the substrate 410.

The substrate 410 may be positioned on a heat exchanging device 415configured to control over all temperature of the substrate 410. Theheat exchange device 415 may be positioned on one or more conventionalelectrical actuators 417 (e.g., linear motor, lead screw and servomotor), which may be part of a separate precision stage (not shown),configured to control the movement and position of substrate 410.Conventional precision stages that may be used to support and positionthe substrate 410, and the heat exchanging device 415, may be purchasedfrom Parker Hannifin Corporation, of Rohnert Park, Calif.

In one aspect, the anneal region 412 is sized to match the size of thedie 413 (e.g., 40 dice are shown in FIG. 4), or semiconductor devices(e.g., memory chip), that are formed on the surface of the substrate410. In one aspect, the boundary of the anneal region 412 is aligned andsized to fit within the “kurf” or “scribe” lines 410A that define theboundary of each die 413.

Sequentially placing anneal regions 412 so that they only overlap in thenaturally occurring unused space/boundaries between die 413, such as thescribe or kurf lines 410A, reduces the need to overlap the energy in theareas where the devices are formed on the substrate 410 and thus reducesthe variation in the process results between the overlapping annealregions 412.

In one embodiment, prior to performing the annealing process thesubstrate 410 is aligned to the output of the energy source 420 usingalignment marks typically found on the surface of the substrate 410 andother conventional techniques so that the anneal region 412 can beadequately aligned to the die 413.

The energy source 420 is generally adapted to deliver electromagneticenergy to preferentially melt certain desired regions of the substratesurface. Typical sources of electromagnetic energy include, but are notlimited to an optical radiation source (e.g., laser), an electron beamsource, an ion beam source, and/or a microwave energy source.

In general, the substrate 410 is placed within an enclosed processingenvironment (not shown) of a processing chamber (not shown) thatcontains the heat exchanging device 415. The processing environmentwithin which the substrate 410 resides during processing may beevacuated or contain an inert gas that has a low partial pressure ofundesirable gases during processing, such as oxygen.

In one embodiment, it may be desirable to control the temperature of thesubstrate 410 during thermal processing by placing a surface of thesubstrate 410, illustrated in FIG. 4, in thermal contact with asubstrate supporting surface 416 of the heat exchanging device 415. Theheat exchanging device 415 is generally adapted to heat and/or cool thesubstrate 410 prior to or during the annealing process. In thisconfiguration, the heat exchanging device 415, such as a conventionalsubstrate heater available from Applied Materials Inc., Santa Clara,Calif., may be used to improve the post-processing properties of theannealed regions of the substrate 410.

In one embodiment, the substrate may be preheated prior to performingthe annealing process so that the energy required to reach the meltingtemperature is minimized, which may reduce any induced stress due to therapid heating and cooling of the substrate 410 and also possibly reducethe defect density in the resolidified areas of the substrate 410. Inone aspect, the heat exchanging device 415 contains resistive heatingelements 415A and a temperature controller 415C that are adapted to heata substrate 410 disposed on the substrate supporting surface 416. Thetemperature controller 415C is in communication with the controller 421.

In one aspect, it may be desirable to preheat the substrate to atemperature between about 20° C. and about 750° C. In one embodiment,where the substrate is formed from a silicon containing material it maybe desirable to preheat the substrate to a temperature between about 20°C. and about 500° C. In another embodiment, where the substrate isformed from a silicon containing material it may be desirable to preheatthe substrate to a temperature between about 200° C. and about 480° C.In another embodiment, where the substrate is formed from a siliconcontaining material it may be desirable to preheat the substrate to atemperature between about 250° C. and about 300° C.

In another embodiment, it may be desirable to cool the substrate duringprocessing to reduce any diffusion due to the energy added to thesubstrate during the annealing process and/or increase the regrowthvelocity after melting to increase the amorphization of the variousregions during processing. In one configuration, the heat exchangingdevice 415 contains one or more fluid channels 415B and a cryogenicchiller 415D that are adapted to cool a substrate disposed on thesubstrate supporting surface 416. In one embodiment, a conventionalcryogenic chiller 415D, which is in communication with the controller421, is adapted to deliver a cooling fluid through the one or more fluidchannels 415B. In one aspect, it may be desirable to cool the substrateto a temperature between about −240° C. and about 20° C.

During a pulsed laser anneal process, a substrate being processed movesrelative to an energy source so that portions of the substrate areexposed to the energy source sequentially. The relative movement may bea stepping motion. For example, the substrate may be moved to andmaintained at a first position so that a first area on the substrate isaligned with the energy source. The energy source then projects adesired amount of energy toward the first area on the substrate. Thesubstrate is then moved to a second position to a second area with theenergy source. The relative movement between the substrate and theenergy source is stopped temporarily when the energy source projectsenergy to the substrate so that the energy is projected precisely anduniformly to a desired area. However, this stepping motion involvesaccelerating and decelerating in every step which significantly slowsthe down the process.

FIG. 5 schematically illustrates a top view of a substrate 410 thatcontains forty square shaped dice 413 that are arranged in an array. Thedice 413 are separated from one another by areas marked by scribe lines410A. Energy projection region 520A indicates the area over which energysource 420 (shown in FIG. 4) is adapted to deliver an energy pulse. Ingeneral, the energy projection region 520A may cover an area equal to orgreater than the area of each die 413, but smaller than the area of eachdie 413 plus the area of the surrounding scribe lines 410A, so that theenergy pulse delivered in the energy projection region 520A completelycovers the die 413 while not overlapping with the neighboring dice 413.

To perform the annealing process on multiple dice 413 spread out acrossthe substrate surface, the substrate and/or the output of the energysource 420 needs to be positioned and aligned relative to each die. Inone embodiment, curve 520B illustrates a relative movement between thedies 413 of the substrate 410 and the energy projection region 520A ofthe energy source 420, during a sequence of annealing process as thatare performed on each die 413 on the surface of the substrate. In oneembodiment, the relative movement may be achieved by translating thesubstrate in x and y direction so that they follow the curve 520B. Inanother embodiment, the relative movement may be achieved by moving theenergy projection region 520A relative to a stationary substrate 410.

Additionally, a path different than 520B may be used to optimizethroughput and process quality depending on a particular arrangement ofdies.

In one embodiment, during an annealing process, the substrate 410 movesrelative to the energy projection region 520A, such as shown by curve520B of FIG. 5. When a particular die 413 is positioned and alignedwithin the energy projection region 520A, the energy source 420 projectsa pulse of energy towards the substrate 410 so that the die 413 isexposed to a certain amount of energy over a defined duration accordingto the particular anneal process recipe. The duration of the pulsedenergy from the energy source 420 is typically short enough so that therelative movement between the substrate 410 and the energy projectionregion 520A does not cause any “blur”, i.e. non uniform energydistribution, across each die 413 and it will not cause damage to thesubstrate.

A substrate implanted with B₁₅ ions may be annealed using a sub-meltanneal process involving rapid repeated heating and cooling of implantedregions. FIG. 6 is a flow diagram summarizing a method 600 according toanother embodiment. At 602, a substrate surface is implanted with boronmacromolecules according to any desired embodiment. At 604, theimplanted portion is annealed by exposure to pulses of electromagneticenergy. The pulses of electromagnetic energy rapidly heat and cool theimplanted portion repeatedly to anneal the substrate.

In one embodiment, the pulses of electromagnetic energy comprise atleast about 30 pulses of electromagnetic energy of substantially thesame energy flux and duration. In one embodiment, the number of pulsesmay be at least about 30, or at least about 50, or at least about 100,such as between about 30 and about 100,000 pulses, or between about 50and about 10,000 pulses, or between about 100 and about 1,000 pulses, orbetween about 200 and about 500 pulses. In one embodiment, the energyflux of each pulse is between about 0.1 J/cm² and about 2.0 J/cm², suchas between about 0.2 J/cm² and about 1.0 J/cm², for example about 0.25J/cm². In one embodiment, the pulses comprise laser light. Each pulsemay have duration between about 1 nsec and about 10 μsec, such asbetween about 10 nsec and about 100 nsec, for example about 20 nsec. Thenumber of pulses needed will generally be inversely proportional to thefluence and duration of each pulse.

Each pulse of electromagnetic energy accomplishes a micro-anneal cyclein the energized area of the substrate. Unfragmented boron clusters arebroken up, and individual boron and silicon atoms are moved fractions ofa unit cell dimension with each pulse. Boron and silicon atoms occupyingcrystal lattice positions do not receive enough energy from each pulseto dislodge them, but those atoms occupying spaces between crystallattice locations are moved incrementally toward unoccupied latticepositions. Incident energy flux between pulses declines to allow energyfrom each pulse to dissipate through the crystal lattice before the nextpulse is delivered. In one embodiment, incident energy flux may declineto near zero between pulses. In another embodiment, incident energy fluxdeclines to allow net energy flux out of the anneal zone. Thus, whilestandard sub-melt techniques require exposing boron-doped substrates tospikes of radiation lasting 20 μsec or more, repeated short pulses mayaccomplish an anneal process at much lower total durations and powerrequirements. The period of time between each pulse relative to theduration of each pulse may be between about 50% and about 200%, such asbetween about 100% and about 150%, for example about 125%. A rest periodbelow about 100% of pulse duration allows the net energy balance of theimplanted region to decline to a non-zero level below the peak energydensity experienced during a pulse before the next pulse begins. A restperiod above about 125% of a pulse duration allows the net energybalance to return to a rest state prior to the next pulse.

In one example, a substrate was implanted with B₁₈ ions to a dose of2×10¹⁵ cm⁻² at an equivalent boron ion energy of 500 eV. After 30 pulseswith a 20 nsec laser delivering 0.234 J/cm² at a wavelength of 532 nmover a total duration of about 1.4 μsec, R_(s) was about 500Ω. After1000 pulses over a duration of about 45 μsec, R_(s) was about 400Ω.

In another example, a substrate was implanted with B₁₈ ions at a similardose and ion energy. After 300 pulses with a 20 nsec laser delivering0.234 J/cm² at a wavelength of 532 nm over a total duration of about13.5 μsec, boron ion concentration of 10¹⁹ cm⁻³ was found at a depth ofabout 147 Å, with concentration profile at that depth of about 5 Å/dec.

While the foregoing is directed to embodiments of the invention, otherand further embodiments of the invention may be devised withoutdeparting from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

1. A method of treating a substrate, comprising: disposing the substratein a processing chamber; forming a plasma from a vapor of boronmacromolecules and a carrier gas in the processing chamber; immersingthe substrate in the plasma; implanting boron from the plasma into asurface of the substrate; and subjecting the implanted surface to a meltanneal process.
 2. The method of claim 1, wherein the boronmacromolecules comprise clusters containing at least sixteen boronatoms.
 3. The method of claim 1, wherein forming a plasma from the vaporof boron macromolecules and the carrier gas comprises coupling RF powerbetween about 100 W and about 500 W into the vapor of boronmacromolecules and the carrier gas.
 4. The method of claim 3, whereinimplanting the boron from the plasma into the surface of the substratecomprises applying an electrical bias to the substrate between about 100V and about 300 V.
 5. The method of claim 3, wherein flowing the vaporof boron macromolecules through the processing chamber comprises pulsingthe vapor into the processing chamber.
 6. The method of claim 1, whereinforming the plasma from the vapor of boron macromolecules and thecarrier gas comprises pulsing the vapor of boron macromolecules into thecarrier gas.
 7. The method of claim 1, wherein the melt anneal processis a pulsed laser process.
 8. The method of claim 7, wherein the meltanneal process comprises crystallizing the melted portion of thesubstrate surface.
 9. A method of treating a substrate, comprising:forming a plasma of a gas mixture comprising a carrier gas and boronmacromolecules inside a processing chamber; exposing the substrate tothe plasma inside the processing chamber; and then annealing successiveportions of the substrate in a laser annealing process.
 10. The methodof claim 9, wherein the boron macromolecules comprise octadecaborane.11. The method of claim 9, wherein the plasma is an inductive plasma.12. The method of claim 11, wherein forming the plasma comprisesapplying electrical energy to the gas mixture at a power level above alevel that ionizes the boron macromolecules and below a level thatfragments the boron macromolecules.
 13. The method of claim 11, whereinthe gas mixture is formed by pulsing the boron macromolecules into thecarrier gas.
 14. The method of claim 9, wherein annealing successiveportions of the substrate comprises melting and recrystallizing eachsuccessive portion of the substrate.
 15. The method of claim 14, whereinthe boron macromolecules comprise octadecaborane and the plasma is aninductive plasma.
 16. The method of claim 15, wherein forming the plasmacomprises applying electrical energy to the gas mixture at a power levelabove a level that ionizes the boron macromolecules and below a levelthat fragments the boron macromolecules, and exposing the substrate tothe plasma comprises applying an electrical bias to the substrate. 17.The method of claim 16, wherein the laser annealing process is a pulsedlaser process.